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Transcranial magnetic resonance (MR)-guided high-intensity focused ultrasound (tcMRgHIFU) implies a novel, noninvasive treatment strategy for various brain diseases. Nine patients with chronic neuropathic pain were treated with selective medial thalamotomies. Precisely located thermal ablations of 4mm in diameter were produced at peak temperatures of 51°C to 60°C under continuous visual MR guidance and MR thermometry. The resulting lesions are clearly visible on follow-up MR imaging. All treatments were well tolerated, without side effects or neurological deficits. This is the first report on successful clinical application of tcMRgHIFU in functional brain disorders, portraying it as safe and reliable for noninvasive neurosurgical interventions. Ann Neurol 2009;66:858-861 [ABSTRACT FROM AUTHOR]

Computing the visibility of out-door scenes is often much harder than of in-door scenes. A typical urban scene, for example, is densely occluded, and it is effective to precompute its visibility space, since from a given point only a small fraction of the scene is visible. The difficulty is that although the majority of objects are hidden, some parts might be visible at a distance in an arbitrary location, and it is not clear how to detect them quickly. In this paper we present a method to partition the viewspace into cells containing a conservative superset of the visible objects. For a given cell the method tests the visibility of all the objects in the scene. For each object it searches for a strong occluder which guarantees that the object is not visible from any point within the cell. We show analytically that in a densely occluded scene, the vast majority of objects are strongly occluded, and the overhead of using conservative visibility (rather than visibility) is small. These results are further supported by our experimental results. We also analyze the cost of the method and discuss its effectiveness. [ABSTRACT FROM AUTHOR]